A number, → real or → complex,
that is a → root of a
→ non-zero polynomial equation
whose → coefficients are all → rational.
For example, the root x of the polynomial
x^{2} - 2x + 1 = 0 is an algebraic number, because the
polynomial is non-zero and the coefficients are rational numbers.
The imaginary number i is algebraic, because it is the solution to
x^{2} + 1 = 0.

The total number of → protons
and → neutrons
in the → nucleus
of an → atom (symbol A). For
example, Oxygen-16 has a mass number of sixteen, because it has eight
protons and eight neutrons.

The number of → protons in an
→ atomic nucleus (symbol Z). Same as
→ Z-number.
The atomic number is written as a subscript to the left of
the → chemical element
name. For example, the most common isotope of oxygen is shown as
_{8}^{16}O, which has 8 → protons
and its → mass number (A) is 16.

1) The difference between the total number of → baryons and
the total number of → antibaryons in a system of
→ subatomic particles.
It is a measure of → baryon asymmetry and is
defined by the quantity
η = (n_{b} - n_{b-})/n_{γ},
called the → baryon-photon ratio,
where n_{b} is the → comoving number
density of baryons, n_{b-} is the number of
antibaryons, and n_{γ} is that of photons. The value of η for
the → cosmic microwave background radiation (CMBR)
has been very well determined by the → WMAP satellite to be
η = (6.14 ± 0.25) x 10^{-10}. The baryon number is assumed to be
constant. The photons created in
stars amount to only a small fraction, less than 1%, of those in the CMBR.
2) A property of an → elementary particle represented by a
→ quantum number. It is
equal to +1 for a baryon and -1 for an antibaryon.
→ Bosons, → leptons, and
→ mesons have a baryon number B = 0.
→ Quarks and → antiquarks
have baryon numbers of B = +1/3 and -1/3, respectively.
The baryon number is → conserved in all observed types of
particle-particle interaction.

A → numeral system that has 2 as its base and uses
only two digits, 0 and 1. The positional value of each digit in a binary number
is twice the place value of the digit of
its right side. Each binary digit is known as a bit. The decimal numbers from 0 to 10
are thus in binary 0, 1, 10, 11, 100, 101, 110, 111, 1000, 1001, and 1010.
And, for example, the binary number 11101_{2} represents the decimal number
(1 × 2^{4}) + (1 × 2^{3})
+ (1 × 2^{2}) + (0 × 2^{1}) + (1 × 2^{0}),
or 29. In electronics, binary numbers are the flow of information in the form
of zeros and ones used by computers. Computers use it to manipulate and store all of
their data including numbers, words, videos, graphics, and music.

An ordinary number such as 0, 1, 2, or 3, as opposed to an
→ ordinal number
such as 1st, 2nd, or 3rd. Cardinal numbers can be → zero
or → positive
and are used for counting the things that are assumed to be not divisible.

A quantity expressed as the sum of two or more quantities of differing units.
For example 5 hours and 15 minutes or 4 meters and 20 centimeters.
→ composite number.

Number theory:
An → integerN if there exists a
→ right triangle with → rational sides so
that the area of the triangle is N. For example, the number N = 6,
because of the 3-4-5 triangle.

The conjugate of a → complex number, expressed by
ū = a - bi. The complex number and its conjugate have the same real part.
Same as → complex conjugate.

1) Crystallography: The
number of nearest neighbors of an atom or ion in a → crystal lattice.
A large coordination number indicates that the structure is more closely packed.
2) Chemistry: The number of atoms, ions, or molecules surrounding a central
atom or ion in a complex.

Unit of the analog-to-digital conversion system of a CCD apparatus. For example
a 16 bit system may use a maximum of 65536 DN. The acronym ADU, for analog-to-digital
unit, is also used.